[PATCH can-next v3 0/3] Introduce diag support for CAN

[Filippo Storniolo <fstornio@redhat.com>]

In the current state of the art, it is not possible for userspace to use
tool like ss(8) to query open AF_CAN sockets.

This patch series adds the netlink can_diag interface for AF_CAN. Userspace
is  now able to send a netlink request to request information about open
AF_CAN sockets that are retrieved by the can-diag.ko module.

Patch 1 is a fix that is mandatory to the correct behaviour of the diag
module: the field sk_protocol is not assigned during `can_create()` instead
of being assigned only in case the CAN socket belong to the j1939 transport
protocol. This is needed to the correct filtering of the can diag module.

Patch 2 introduces a list per network namespace containing open CAN sockets.
The list is protected by a mutex.
CAN sockets are added in `can_create()` to the list and removed from it
in the `release()` calls defined for each transport protocol.

Patch 3 is the core patch that introduces the userspace structures to query
and receive netlink messages for CAN sockets and the actual CAN diag module.
The latter will use the userspace structures defined in <linux/can/diag.h>
to filter and retrieve open CAN sockets.

In the current implementation, every CAN sockets in the list is
returned to the userspace, however a filtering could be implemented:
Userspace could possibly request only bound CAN sockets or CAN sockets
belonging to a specific transport protocol (raw, iso-tp, j1939, bcm)
and so on.

An example of the output given by ss -cpe:

Netid                     Recv-Q                 Send-Q                                 Local Address:Port                                   Peer Address:Port                 Process                                                                 
CAN_ISOTP                 0                      0                                              vcan1:1110                                          vcan1:291                   uid:1001 ino:50324 sk:0 users:(("can2",pid=9210,fd=4))                 
CAN_ISOTP                 0                      0                                              vcan1:291                                           vcan1:1110                  uid:1001 ino:50323 sk:0 users:(("can2",pid=9210,fd=3))

---
Changes in v3:
- Rebased to latest net-next
- Changed no-op functions from #define to static inline
  (Marc Kleine-Budde)
- In struct can_diag_req, sdiag_protocol changed from
  __u8 to __u16. Padding changed accordingly
- Added	CDIAG_SHOW_UID filter in UAPI header and implemented
  filter as netlink attribute in diag module.
- Split sockaddr_can into individual netlink attributes
  for isotp and j1939 respectively, instead of binary-encoding
  it into a single attribute (Sashiko-bot / Marc Kleine-Budde)
- Fixed indentation in /netns/can.h (Marc Kleine-Budde)
- Link to v2: https://lore.kernel.org/r/20260806-feat-can-diag-v2-0-832597ee4cb9@redhat.com

Changes in v2:
- Rebased to latest net-next
- Added a patch, suggested by sashiko-bot, that fixes an attempt
   to lock an uninitialized mutex
- Link to v1: https://lore.kernel.org/r/20260610-feat-can-diag-v1-0-021e3f1631a0@redhat.com

Change w.r.t. RFC:
- header relocation, from linux/can_diag.h to linux/can/diag.h
  (Oliver Hartkopp)
- file renaming, from net/can/can-diag.c to net/can/diag.c
  (Oliver Hartkopp)
- guard renaming, from _UAPI__CAN_DIAG_H__ to _UAPI_CAN_DIAG_H_
  (Oliver Hartkopp)
- handled J1939 addressing in sockaddr_can
  (Oliver Hartkopp)
- Link to RFC: https://lore.kernel.org/linux-can/20260402-feat-can-diag-v1-0-245b56434c1b@redhat.com/

---
Davide Caratti (1):
      af_can: ensure sk_protocol is always set on socket creation

Filippo Storniolo (2):
      af_can: store socket pointers in struct netns_can
      can: add can diag interface

 MAINTAINERS                   |   1 +
 include/linux/can/core.h      |  11 +++
 include/net/netns/can.h       |   6 ++
 include/uapi/linux/can/diag.h |  50 +++++++++++
 net/can/Kconfig               |  10 +++
 net/can/Makefile              |   3 +
 net/can/af_can.c              |  51 +++++++++++
 net/can/bcm.c                 |   2 +
 net/can/diag.c                | 203 ++++++++++++++++++++++++++++++++++++++++++
 net/can/isotp.c               |   2 +
 net/can/j1939/socket.c        |   3 +-
 net/can/raw.c                 |   2 +
 12 files changed, 343 insertions(+), 1 deletion(-)
---
base-commit: 6ebcf5074cff0402730c6981d2397139fee6322d
change-id: 20260529-feat-can-diag-d7acbf5e22c2

Best regards,
-- 
Filippo Storniolo <fstornio@redhat.com>